Final answer:
Two coats of Sika Primer 207 are used on porous, rough, or difficult-to-bond surfaces like plastics and metals to ensure optimal adhesion, with a dry touch time between coats.
Step-by-step explanation:
You should use two coats of Sika Primer 207 when preparing surfaces for bonding applications where the substrates are either porous, have a rough texture, or are difficult to bond materials like plastics, metals, or painted surfaces.
Sika Primer 207 serves as an adhesion promoter, and it is especially important to apply a second coat on surfaces that may absorb the primer or when recommended by the manufacturer for optimal bonding strength.
For effective application, the first coat should be applied in a thin, continuous film and allowed time to become touch-dry before applying the second coat. This waiting time between coats ensures proper drying and effective primer layering.